A portable air compressor, highly useful in both industrial and agricultural applications, usually comprises a compressor pump, a drive unit for the pump, and a storage tank. Most frequently, the tank is mounted upon wheels to provide portability, with the compressor pump and its drive unit mounted above the tank on a frame affixed to the tank. The compressor is usually equipped with a pressure gauge, a pressure regulator, a relief valve, control switches, and other necessary fittings.
In the conventional construction, with the compressor pump and drive unit mounted on top of the storage tank, there is excellent accessibility to the pump and drive unit for service and maintenance purposes. However, this construction is inherently top-heavy and unstable because the pump and drive unit are substantially heavier than the tank, leaving much to be desired from the standpoint of occupational safety. On the other hand, it has been known to mount the tank on a frame with the pump and its drive unit supported within the frame below the tank. This inverted construction greatly improves the stability of the portable air compressor, placing its center of gravity at a safe low level. However, accessibility of the compressor pump and the drive unit for service and maintenance purposes is materially hampered by the tank. Furthermore, it is quite desirable to enclose the pump and drive unit for occupational safety; any such enclosure further reduces accessibility so that service becomes inconvenient and time-consuming.
In portable air compressors having the tank mounted above the pump, a sturdy support frame has been considered necessary. Usually, the frame is formed of steel angle members or steel tubes, capable of supporting all of the compressor components and also adapted to withstand the heavy vibration produced by compressor operation. A frame of this kind is relatively expensive and adds materially to the overall cost of the air compressor, as compared with a sheet metal construction. However, it has not heretofore been considered that a sheet metal housing affords adequate rigidity and strength under the severe vibration conditions encountered in the operation of an air compressor.